1. Field of the Invention
The present invention relates to a layered trace configuration which prevents the formation of metal polymer residues and allows for removal of oxide polymer residues from a via with substantially no damage to the via or underlying structures carried on a semiconductor substrate.
2. State of the Art
Higher performance, lower cost, increased miniaturization of components, and greater packaging density of integrated circuits are ongoing goals of the computer industry. One commonly used technique in the fabrication of integrated circuits involves stacking of multiple layers of active and passive components one atop another to allow for multilevel electrical interconnection between devices formed on each of these layers. This multilevel electrical interconnection is generally achieved with a plurality of metal-filled visa (xe2x80x9ccontactsxe2x80x9d) extending through dielectric layers which separate the component layers from one another. These visa are generally formed by etching through each dielectric layer by etching methods known in the industry, such as plasma etching and reactive ion etching. A fluorinated gas, such as CF4, CHF3, C2F6, CH2F2, SF6, or other freons, and mixtures thereof, in combination with a carrier gas, such as Ar, He, Ne, Kr, O2, or mixtures thereof, are usually used as the etching gas for these etching methods. A problem with such etching methods is that at least one layer of residue forms in the visa as a result of the etching process.
An exemplary method for forming a via through a dielectric layer is illustrated in FIGS. 10-13. It should be understood that the figures presented in conjunction with this description are not meant to be actual cross-sectional views of any particular portion of an actual semiconductor device, but are merely idealized representations which are employed to more clearly and fully depict the process of this typical method than would otherwise be possible.
FIG. 10 illustrates an intermediate structure comprising a semiconductor substrate 200 bearing a dielectric or insulating layer 202 (such as an oxide-silicon dioxide, etc.) having a metal-containing trace or pad 204 of aluminum, copper, aluminum/copper alloys, or the like, formed thereon. The term xe2x80x9csemiconductor substratexe2x80x9d is used herein to denote any solid semiconductor surface, such as is provided by a silicon or gallium arsenide wafer, or a layer of such material formed on glass, ceramic, sapphire, or other supporting carrier, as known in the art, and includes such semiconductor surfaces bearing an insulating layer thereon. The term xe2x80x9ctracexe2x80x9d is used herein to denote any metallized structure in a semiconductor device including, but not limited to, conductive traces and conductive pads.
A barrier layer 206 (such as titanium nitride) is deposited over the metal-containing trace or pad 204 and an interlayer dielectric 208 (such as silicon dioxide) is disposed over the barrier layer 206. As shown in FIG. 11, the interlayer dielectric 208 is masked with a resist material 212, which is then patterned to define a via location. A partial via 214 is then selectively etched with a fluorinated gas down to the barrier layer 206, which acts as an etch stop. The etching of the partial via 214 results in a first residue layer 216 of a carbon-fluorine based polymer containing residue of the interlayer dielectric 208 (xe2x80x9coxide polymerxe2x80x9d) coating the sidewall 218 of the partial via 214, as shown in FIG. 12.
The barrier layer 206 at the bottom of partial via 214 is then etched to expose the metal-containing trace or pad 204 and form a full via 222, as shown in FIG. 13. However, due to the variation in the thickness of the interlayer dielectric 208 from the center of a wafer to the edge (usually between 4000 and 5000 xc3x85), an over-etch is applied, such that the via will usually extend through the barrier layer 206 and into the metal-containing trace or pad 204. When the barrier layer 206 and metal containing trace or pad 204 are etched, a second residue layer 224 (xe2x80x9cmetal polymerxe2x80x9d) of a carbon-fluorine based polymer including metal etched from the metal-containing trace or pad 204, as well as any metal components in the barrier layer 206, such as the titanium in a titanium nitride barrier layer, is formed over the first residue layer 216 and the exposed surface 226 of the metal-containing trace or pad 204, also shown in FIG. 13.
It is, of course, understood that a single etch could be performed to expose the metal-containing trace or pad 204, which etch would result in a single residue layer. However, even if a single etch were performed, the single residue layer would still have a portion of the residue layer adjacent the via sidewall 218 containing predominantly oxide polymer and a portion adjacent the via aperture and the bottom of the via containing predominantly metal polymer.
Residue layers, such as first residue layer 216 and second residue layer 224, which coat the full via, are very difficult to remove. These residue layers may be removed by dipping the structure in a phosphoric acid solution; and, although this technique is effective in removing most of the residue layers, the residue layers are still not completely removed. The portion of the residue still remaining after the phosphoric acid dip adversely affects the conductivity of contacts subsequently formed in the full via 222. It is noted, that although extending the residence time of the semiconductor substrate structure in the phosphoric acid will effectively remove all of the residue layer(s), the increased residence time also results in damage to the metal-containing trace or pad 204.
Thus, it can be appreciated that it would be advantageous to develop a technique to form a via which prevents the formation of metal polymer residues and allows for removal of oxide polymer residues from the via without substantial damage to the metal-containing trace or pad while using commercially-available, widely-practiced semiconductor device fabrication techniques.
The present invention relates to a layered trace comprising a conductive trace capped with a silicide material. When such a layered trace is used in a multilayer semiconductor structure, it allows for non-damaging removal of any oxide polymer residues forming in visa used to electrically connect the various layers through dielectric layers separating them, and eliminates or greatly reduces the formation of metal polymer residues in the visa. This results in better contact reliability.
One embodiment of forming an interlayer contact according to the present invention involves providing a conductive layer deposited over a semiconductor substrate. A substrate dielectric or insulating layer preferably separates the semiconductor substrate from the conductive layer. A silicide layer, such as tungsten silicide, cobalt silicide and the like, is disposed over the conductive layer. An optional barrier layer, such as a thin film of titanium, may be disposed between the conductive layer and the silicide layer to prevent silicon molecules from the silicide layer from migrating into and contaminating the metals in the conductive layer.
A first resist material is patterned over the silicide layer and the silicide layer, the barrier layer, and the conductive layer are etched and any remaining first resist material is removed to form a layered trace or pad. An interlayer dielectric is deposited over the layered trace and the substrate dielectric. A second resist material is then patterned over the interlayer dielectric layer such that an opening in the second resist material is positioned over the layered trace.
The interlayer dielectric layer is then etched, preferably using an oxide etch selectively stopping on the silicide layer, through the opening in the second resist material to form a via through the interlayer dielectric layer to the silicide layer of the layered trace. The etching of the via through the interlayer dielectric layer creates an oxide polymer residue layer on sidewalls of the via. As used herein, the term xe2x80x9csidewallxe2x80x9d of a via encompasses both a single, continuous sidewall such as may define a round or circular via, as well as a plurality of sidewalls defining a via of other cross-section. The presence of the oxide polymer residue layer is a natural consequence of the etching of the via and, since the etching gas generally comprises a fluorinated gas, the oxide polymer residue layer is usually a carbon-fluorine based polymer containing residue of the interlayer dielectric.
The oxide polymer residue layer and any remaining second resist material are preferably removed by any suitable known technique. At this point, an upper-layer trace or contact can be formed over the interlayer dielectric and into the via to make electrical contact with the silicide layer of the layered trace. However, if electrical resistance is a concern, a highly selective etch can be used to subsequently remove the silicide layer in the via, which will reduce contact resistance by bringing subsequently deposited conductive material into direct contact with the barrier layer or the conductive layer. An upper-layer trace or a contact may be completed by depositing a conductive material into the via.
It is, of course, understood that the layered trace may be formed on an interlayer dielectric above the semiconductor substrate with another interlayer disposed over the layered trace and the interlayer dielectric, with a contact being formed to the layered trace in a manner described above.